Dewaxing of motor fuels



7 1937- .1. K. ROBERTS ET AL DEWAXING OF MOTOR FUELS Filed Aug. 31, 1931 Patented Apr. 20, 1937 UNITED STATES PATENT FOFFICE nnwaxmc or MOTOR FUELS Application August 31, 1931, Serial No. 560,316

10 Claims.

This invention relates to the dewaxing of motor oils and it pertains more particularly to a dewaxing system using a combined diluent-refrigerant of the butane-propane type.

Some waxes, usually those of the so-called .paraffin distillate range, contain relatively low melting point waxes which, on cooling, form well defined crystals that may be filtered or sweated for the removal of oil therefrom. Other waxes, usually those found in steam refined residuums (heavy motor base stock) contain relatively high melting point waxes (ceresins which, on chilling, separate out from filter naphtha into fiocculent masses which may be settled but which cannot be filtered. Between the paraflln distillate and the motor base stock there are slop wax cuts which contain mixtures of parafiins and ceresins, and it is extremely difl'lcult to separate these slop waxes from the 011 because their amorphous structure prevents filtration and their semi-crystalline structure prevents eflective settling. Overhead motor base stocks are difiicult to dewax for this reason, and an object of our invention is to provide an improved process for separating waxes from such cuts.

A further object is to provide an improved system for obtaining low pour point motor oils by removing the waxes therefrom. A further object is to reduce refrigerating and heating costs. A further object is to provide a closed system which is so arranged that the diluent and refrigerant may be recovered and recycled, and so thatthe fire hazard may be reduced to a minimum. A further object is to provide an improved system of exchangers, flash drums, compressors, etc. so that desirable temperatures and pressures may be maintained in the various parts of the system. Other objects will be apparent as the detailed description of our invention proceeds.

In carrying out our invention we preferably use a mixture of about 70% butane and 30% propane. The oil is mixed with a small amount of diluent and heated to about 150 F. to effect complete solution, after which it passes through an exchanger and cooler to bring it down to room temperature. A large amount of pre-cooled diluent is then added and the mixture is charged into one of a series of chill chambers. One of the chill chambers is constantly being filled, another is being cooled and a third is being emptied so that the process is continuous and there is no interruption in the feed to the filters or through the exchangers. Chilling is accomplished by removing vapors from the chamber at any desired rate, and the cold wax slurry is then filtered to remove the wax therefrom. The cold filtrate is then passed through an exchanger to pre-cool the diluent entering the chill chambers. The diluent is finally removed from the wax and oil, and returned to the system. The invention will be more clearly understood from the following description and from the accompanying drawing wherein we have illustrated our system by means of a flow sheet on which several parts are shown diagrammatically.

The oil to be dewaxed may be a heavy petroleum distillate or steam-refined residuum, it being understood, of course, that different amounts of diluent will be used for oils of various compositions, viscosities, etc. In our preferred embodiment we will describe the dewaxing of motor base stock produced as a distillate from Mid- Continent petroleum, such as oil having a flash point of about 470 F. and a viscosity at 210 F. of about '70-'75 se'c. Saybolt. Steam-refined residuums may be dewaxed, but the invention is particularly applicable to overhead heavy lubricants, because these oils cannot be readily dewaxed by other methods.

The diluent is preferably about 30 parts by weight of propane mixed with parts of butane. This is by way of example only, and it is understood that various mixtures of light hydrocarbons, including ethane, propane, butane, isobutane, pentane, light unsaturated hydrocarbons, etc., may be used. This mixture is usually defined by its vaporpressure, which is preferably about pounds per square inch at F.

The butane-propane mixture at about 80 pounds pressure and 85 F. temperature is withdrawn from storage tank l0 through pipe ll, pump l2, pipe l3, and valve I 4. It is mixed with the waxy oil mixture introduced by pipe l5, and. this mixture is passed through exchanger l6, pipe I I, steam heater I8 and pipe l9 to mixer 20. The plant may be designed to yield 1000 barrels per day of finished oil, in which case about 1175 barrels of oil are charged into the system. About 4000 or 5000 barrels of the diluent-refrigerant mixture are circulated with this amount of oil but this mixture is continuously cycled through the system so that the total amount of diluent required is considerably less than this.

About 10% or 20% of the diluent feed is initially mixed with the oil and heated to effect complete solution of the wax. The mixture entering exchanger H5 at about 85 F. leaves it at F., and leaves the steam heater at about pounds per square inch. The mixer may be of any conventional type, and in some cases we have found that it may be nothing more than 5 a baflled or hollow'chamber. The mixture at 150 is again passed through exchanger l6 wherein it is cooled to about 126 F., after which it is introduced-by pipe 22 into water cooler 23 wherein it is cooled to about 80 F.

From the water cooler partially diluted oil is mixed with the additional required amount of the diluent mixture supplied through valve 26, pipe 21 and exchanger 28. In exchanger 28 the remaining 80% or 90% of the diluent is cooled to a very low temperature and the pre-cooled diluent lowers the temperature of the oil-wax mixture to about 40 F. after which it is introduced into one of the chill chambers 30, 33 or 36. The mixture may be introduced through valve 29 into chamber 36, through pipe 3| and valve 32 into chamber 33, or through pipe 34 and valve 35 into chamber 36. One of these chambers is being filled while another is being chilled and the third is being emptied so that there is no interruption of 'fiow through the filters or exchangers. Vapors may be withdrawn from the top of the chambers through valves 31, 38'

and 39 respectively into manifold 40, from which they are withdrawn by pipes 4| and 42, compressor 43 and pipe 44, passed through Water cooler 45 and finally discharged by pipe 46 into storage chamber l0. Y

The mush or suspension of wax crystals in the diluted oil may be withdrawn from the base of the chambers through valves 41, 48 or 49 respectively, manifold 50, pipe 5|, pump 52, and pipe 53 to filters 54. It is understood, of course,

that fluid pressure may be used to force this' mush or slurry into the filter chambers instead of a mechanical pump. The filters may be of closed, continuous pressure type, but the filter structure per se forms no part of the present invention and it will not be described in detail.

The chill chamber which is being filled is closed at the top and bottom, the pressure of incoming liquids causing the condensation of vapors which may be present therein. The chamber which is being cooled is closed at. the bottom and opened at the top so that the vapors are removed at a rate to give the desired chilling rate, which maybe about 150 F. per hour and the mixture in the chamber is cooled to a final temperature of about 30 F. After cooling the top valve is closed and the bottom valve opened so that the mixture can be forced through the filters. It is understood, of course, that all of the exchangers, chillers, filters, pipes, etc. are properly insulated to prevent refrigeration losses.

The wax iscontinuously removed from filters 54 by a screw conveyor or other suitable means 55, which-discharges said wax into heater 56 which contains steam coils 51 or other heating means. The butane and propane is vaporized from the melted wax, the wax being withdrawn from the base of the heater through pipe 56 and the vapors being withdrawn through pipes 59 and 42 by compressor 43, which forces them through pipe 44, cooler 45 and pipe 46 into storage chamber I0.

The filtrate from filters 54 is discharged through pipes 60 into receiver 6|. The vapors which may be generated due to warming up the solution during filtration are continuously removed from this receiver by pipe 53 in 150 F. under a gage pressure of about 160-165 amounts regulated by pressure control valve 63, the removed vapors being withdrawn through pipes 64, 4| and 42 to compressor 43. The dewaxed mixture at a temperature of -15 to -30 F. is conducted through pipe 65, pump 66 and pipe 61 to heat exchanger 28 wherein it cools the larger portion of incoming diluent as hereinabove described. Where filter operations can be conducted in a smoothly continuous manner, the receiver 6| may be bypassed and the filtrate led through line 65a to pump 66. It is important to note that the diluent is cooled before it is mixed with the wax solution, so that a proper crystallization will be efiected and so that the wax crystals will not interfere with the cooling system.

The oil-diluent mixture leaves exchanger 28 through pipe 68 and is then conducted through exchanger 69and pipe 10 to oil heater II wherein the oil is heated by steam coil 12 or other means. Butane and propane vapors are forced through pipe 13 into pipe 44, and they are then condensed by cooler 45 and returnednby pipe 46 to storage tank Hi. It should be noted that heater H is at a pressure of about pounds per square inch so that when the temperature in the top of the heater is about -160 F., the butane-propane vapors will be discharged therefrom and condensed without the need of a compressor. With diluent mixture containing larger proportions of the lower boiling hydrocarbons, e. g. propane, higher pressures will be required.

The finished oil is withdrawn from the base of heater 1| through pipe 14, heat exchanger 69 and pipe 15.

The operation of our process has been described along with the description of the apparatus, but it may be briefly summarized as follows: About two parts of waxy oil are mixed with one part of a butane-propane diluent and passed through an exchanger and a heater to raise its temperature to about 150 F. at which the wax is completely dissolved. The hot mixture is then passed through the heat exchanger so that its heat is transferred to incoming oil and diluent.

After further cooling in cooler 23 it is mixed with about seven or'eight parts of refrigerant diluent liquid which has been cooled in exchanger 23 by the diluted oil from receiver 6 I. The mixture entering the chill chamber consists of about one part oil to four or five parts diluent-refrigerant mixture. While' one chill chamber is being filled another is being chilled by the removal of vapors through the upper valves manifold 40, pipe 4|, compressor 43, etc. and a third chamber is being discharged into the filter through a lower valve manifold 50, pipe 5|, pump 52, .pipe 53. The diluent removed with wax is recovered and pumped back into the system through pipes 59 and 42, and compressor 43. Diluted oil is collected in drum 6|, the vapors being removed through pressure regulator 63, pipes 64, 4| and 42, and compressor 43. The cold filtrate is passed through exchanger 28 to absorb heat from the incoming butane-propane diluent mixture and is then passed through exchanger 69, heater 1 I, and back to exchanger .69, the remainder-of the diluent passing through pipe.'|3 back into the system.

While we have described in detail a preferred embodiment of our invention it is understood that we do not limit ourselves to the specific arrangement, proportions, operating temperatures and pressures, etc. except as defined by the following claims which shall be construed as broad- 1y as the prior art will permit.

We claim:

1. A continuous dewaxing system which comprises three chill chambers, means for dissolvin a waxy oil in a diluent-refrigerant mixture and for selectively introducing said mixture into each one of said chill chambers, means for selectively withdrawing vapors from each one of said chill chambers to effect refrigeration thereof, a filter, means for selectively withdrawing refrigerated liquid containing crystallized wax from each one of said chambers and introducing it into said filter whereby one chamber can be filled while another is chilled and the thirdis emptied so that the means for removing vapors and operating filters may be operated continuously.

2. A method of producing low pour point lubricating oils from heavy wax-bearing petroleum lubricating oil stock, which comprises completely dissolving said heavy wax-bearing stock in a small amount of a liquefied normally gaseous hydrocarbon diluent at an elevated temperature and pressure, cooling the said -solution, separately cooling a large amount of the liquefied normally gaseous light hydrocarbon diluent by heat exchange with cold dewaxed oil solution, adding the separately cooled diluent to the cooled mixture in which the waxy solution has been initially dissolved, chilling resultant mixture, and mechanically separating solidified wax from dewaxed oil solution, heat being supplied from said'large amount of diluent for vaporizing diluent from said dewaxed oil solution whereby the refrigeration effect of the dewaxed oil solution is utilized to cool diluent prior to the mixture of waxy oil therewith.

3. A method of producing low pour point lubricating oils from heavy wax-bearing petroleum lubricating oil stock which comprises admixing said stock with a liquefied normally gaseous diluent, dissolving said heavy wax-bearing stock in said liquefied normally gaseous hydrocarbon diluent at an elevated temperature and pressure,

. adding a large amount of cold normally gaseous hydrocarbon liquid to the mixture, cooling the solution to solidify wax in readily separable form,

4. Themethod of dewaxing a wax-bearing hydrocarbon oil which comprises mixing said oil with a small amount of a diluent consisting essentially of propane and butane at a temperature high enough to obtain solution of the oil and wax in the diluent, separately chilling a larger amount of said diluent to a low temperature, partially chilling the hot waxy oil solution, adding the chilled 7. The method of claim 4 wherein the diluted oil from the mechanical wax separation stage is further chilled by the vaporization of diluent therefrom and wherein this further chilled oil is passed countercurrent to the large amount of diluent to chill it by heat exchange.

8. The method of claim 4 wherein the wax is separated from the diluted oil by filtration and wherein the chilled mixture is transferred to the filtration step without mechanical working.

9. The method of separating wax from a waxbearing lubricating oil stock which comprises mixing said stock with a small amount of a liquefled normally gaseous diluent, heating said mixture to a temperature sufflcient to effect solution of both wax and oil in said diluent, partially chilling said solution, separately chilling a large amount of said diluent to a lower temperature than the partially chilled solution, mixing said partially chilled solution and large amount of oil and introducing said mixture into said chilling zone, further, chilling the mixture in the chilling zone by evaporative cooling to effect substantially complete crystallization of the wax, mechanically separating the wax from diluted oil and removing diluent from the separated wax and diluted oil respectively.

10. The method of claim 9 wherein a large amount of diluent is separately cooled by heat exchange with separated diluted oil subsequent to the separation of wax therefrom and prior to the removal of all of the diluent therefrom.

JOSEPH K. ROBERTS. MORRIS T. CARPENTER.

CERTIFICATE OF CORRECTION.

Patent No. 2,077,712. April 20, 1937.

JOSEPH K. ROBERTS, ET AL.

It is hereby certified that error appears in the above numbered patent requiring correction as follows: In the grant, heading to drawing and printed specification, title of patent, for "THE DEWAXING OF MOTOR FUELS" read THE DEWAXING OF MOTOR OILS; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and. sealed. this 8th day of June, A. D. 1957,

Henry Van Arsdale {5681) Acting Commissioner of Patents. 

